The mammalian pineal gland is a multipotential organ of internal secretion. In addition to melatonin, a large number of peptide hormones have been identified in the pineal in recent years, yet their physiological significance is unknown. Pineal modulation of reproduction is well documented and the mechanism of action of an antigonadotropic hormone(s) is of paramount interest. Although the hormone melatonin is well established as a, or the, pineal antigonadotropin, a large body of evidence suggests that non-indolic, ostensibly polypeptidic antigonadotropic substances are present in mammalian pineal gland extracts as well. The applicants have established methods for the purification of antigonadotropic substance(s) from dilute acetic acid extracts of bovine pineal glands by gel filtration, ultrafiltration, ion exchange, paper and high pressure liquid chromatography. The antigonadotropic substance is inactivated by proteolytic enzymes. When injected into mice and rats this potential hormone retards puberty, inhibits fertility and blocks ovulation. This pineal antigonadotropin also inhibits the postcastration rise in LH in male rats, augments the negative feedback effects of testosterone on LH in mice and lowers LH and PRL levels in intact rats. It may act at hypothalamic levels, through effects on catecholamine synthesis. Methods have been established for preliminary purification of the antigonadotropic substance(s) on a large scale. We propose to continue work in progress on the chemical structure and mechanism of action of this pineal antigonadotropic substance. Sufficient quantities will be purified for structure determination using preparative high pressure liquid chromatography and a peptide sequencer recently acquired by the university in part for this project. When structures are known, synthesis of analogs will be accomplished. During the proposed isolation steps large quantities of substances with neurohypophysial hormone-like and LHRH-like biological activities will accumulate as by-products of the preparative separation techniques employed. These peptides will be purified and characterized.